On Fri, Sep 1, 2023 at 12:29 PM Jonathan Wakely <jwakely.gcc@xxxxxxxxx> wrote: > > On Fri, 1 Sept 2023 at 10:57, Mathieu Malaterre via Gcc-help > <gcc-help@xxxxxxxxxxx> wrote: > > > > Hi all, > > > > I am reading a previous post from Pascal Cuoq(*), and it seems things > > have changed quite a bit in GCC nowadays. I fail to understand how > > FLT_EVAL_METHOD relates to fexcess-precision. Did I miss something? > > > > --- > > > > Here is what I see on my Debian/sid/i386 system: > > It looks to me like the difference is that you're using i386 (welcome, > time traveller!) You might remember me from such films as the powerpc, sparc64 or s390x ;) > where -mfpmath=i387 is the default, so > FLT_EVAL_METHOD=2. I think Pascal's SO answer uses x86_64, where the > default is -mfpmath=sse and so FLT_EVAL_METHOD=0, but changes to 2 > when he uses -mfpmath=i387. I (wrongly) assumed that there was a mapping in between FLT_EVAL_METHOD and -fexcess-precision based on the eps value. For context: I have a math function (log1p impl) which fails with -fexcess-precision=fast but works with -fexcess-precision=standard on i386 ... however I see no difference in the #define(s): % diff -u <(gcc -Wp,-dM -E -c -O2 -fexcess-precision=standard m.c) <(gcc -Wp,-dM -E -c -O2 -fexcess-precision=fast m.c) So I do not have any mechanism to detect invalid compilation flags during build... Thanks anyway for your kind help, -- Mathieu
